Clone BackupManagerService and make Trampoline aware of the clone.

RefactoredBackupManagerService is an exact clone of
BackupManagerService. Trampoline chooses between these two based on
backup_refactored_service_disabled global setting, defaulting to true.

Test: manual: flashed the device, ran `settings put global
backup_refactored_service_disabled 1|0`, verified that correct class was
instantiated, ran bmgr backupnow command to make sure that it works.

Bug: 36850431

Change-Id: I8ef91b928a40aae022f88f07a4126a00b1d5e220